Loop antenna



Aug. 8, 1939. B. L. DOLBEAR LOOP ANTENNA Filed April 5, 1935 2 Sheets-Sheet l J llll II.

X ENTOR' INV BENJAMIN; L. LBEAR BY #62 ATTORNEY 1939- B. L. DOLBEAR ,169,040

OOOOOOOOO NA Filed April 5, 1935 2 Sheets-Sheet 2 INVENTOR BENJAMIN L DOLBEAR ATTO N Patented Aug. 8, 1939 UNITED STATES PATENT OFFICE LOOP ANTENNA tion of Delaware Application April 5, 1935, Serial No. 14,755

2 Claims.

This invention relates to an improved loop antenna which is particularly adapted to radio direction finding.

An object of this invention is to simplify and 5 improve the method of winding an efficient type of multi-turn loop antenna.

Another object of this invention is to provide a multi-turned loop antenna in which the amount of energy picked up by the winding is substantially zero when the loop is turned to the null position.

Another object of this invention is to eliminate or substantially reduce what is known as the cross loop effect by suitable transposition of the Winding.

A feature of this invention is the new and novel method of winding the conductor turns of the loop in such a manner that the complete structure has the appearance of a twist-wound loop.

The multi-turn loop of this invention is particularly desirable for use in aircraft and in marine direction finding employing the null or minimum signal response position as an indication of its direction. The invention is adapted to direction finders having equipment to obtain an efiicient and accurate null position.

The coil or loop antenna known in the prior art is generally wound in the form of an ordinary helix. When such an antenna is used for reception of radio signals in direction finding, it will be found that the position of the loop for least amount of energy pick-up is with the plane of the winding parallel to the wave front of the received signal. This is known as the null position, and in the ordinary type of multi-turn loop, the radio signal pick-up is very seldom exactly zero. The reason a substantially zero pickup is not obtained is that the so-called cross loop eifect or difference in time of arrival of a signal wave front at the two ends of the winding produces a slight potential difference between them. This difference, though it appears very slight, is enough with the highly sensitive receiving equipment used today to produce a residual signal at the minimum signal position. In order to obtain an accurate bearing of a radio signal it is essential that the null indication be sharp and well defined and entirely free from all residual signal due to pick-up induced in the loop winding such as may result from the cross loop efiect.

It is an object of this invention to eliminate or substantially reduce this cross loop effect by introducing a twist or transposition in the winding of the conductor turns in such a manner that 55 the cross-loop effect is balanced or substantially cancelled out. It is proper to arrange the loop winding so that when two or more conductor turns are included, a complete transposition of the wires is made by having each turn cross at a point approximately in the center of the winding. 6

This invention will be better understood by referring to the accompanying drawings, in which Fig. l is a developed view of a multi-turn loop known in the prior art;

Fig. 2 is a developed view of a multi-turn loop 10 With both halves twisted;

Fig. 3 is an elevation of the loop of my invention, the spacers being shown in perspective;

Fig. 4 is a developed View of the loop spacers arranged in their proper sequence; 15

Fig. 5 is a side view of the twist wound loop;

Fig. 6 is a front elevation of Fig. 5;

Fig. 7 is a front elevation of a shielded twist wound loop.

The developed view of the ordinary prior art 20 multi-turn loop of Fig. 1 shows the winding l starting at a point A and passing through spacers B, C, and D, and completing at a point A, which represents one complete turn of the conductor winding. For simplicity of illustration 5 only, a five-turn loop is shown, the conductor turns being indicated as T, U, V. W, X.

Fig. 2 shows the multi-turn loop of my invention wherein the same five-turn loop of Fig. 1 is shown, except that with the points A and A 30 assumed to be fixed spacers, the spacer C is rotated 180 on an axis common to the other spacers. Thus it will be seen that the conductors which,

for the purpose of this illustration, are capable of stretching, will cross a median line M and 35 turn at spacer positions B and D, spacers B and D being omitted to more clearly define the actual positions of the conductor turns.

Referring now in detail to Figs. 3 to '7 of the drawings, the ordinary diamond-shaped loop is 40 shown, although this invention can be equally applied to any other desired shape such as a circular type of loop. The loop winding or conductor l is started at the insulation fixed spacer member 2 at a point 3 and is carried through the 45 floating or central spacer member 4 to a point 5 on another fixed insulation member 6. The point 5 is displaced along the longitudinal axis of the winding from point 3. The winding then progresses through a second floating mem- 50 her 1 to a third fixed insulation member 8 to a fixed point 9, the point 9 being displaced 180 from point 3. The winding continues on passing through a third floating spacer ID to a point H in the fixed spacer [2, the point H being 55 placed 90 from point 9. From this point the winding of conductor l passes through a fourth central spacing member 13 and thence to a point 14, thus completing the first turn. It will be noted that point 14 completes the first conductor turn of the winding. The spacing in the winding is advanced in pitch by an amount to properly space the desired number of turns in the loop. From this advanced point the second conductor turn starts and is wound in a manner similar to that on the first turn, each turn progressing in a clockwise direction equal to that of the space between the conductor turns. After the complete winding of all the turns of the loop, the ends 15 and I! are connected to any suitabale direction finding apparatus.

The developed view of Fig. 4 shows the loop spacers arranged in their proper sequence. For the purpose of more clearly indicating the winding of the loop, only a single conductor turn is shown. In order to show a practical form of loop, the winding is assumed to contain 16 turns. It will be noted in Figs. 3 and 4 that the floating spacers have a diameter equal to the minor axis of the ellipse-like arrangement of holes. The purpose of employing this central spacer is to maintain the diameter of the loop winding at this point substantially equal to the diameter at the corner spacers. Although this loop is shown as open cage-like winding, it is to be understood that in the actual application a suitable metallic shield may surround the winding as shown by Fig. '7.

Having fully described this invention, I claim:

1. A direction finder loop antenna having its winding of conductor turns transposed to give substantially zero energy pickup when said loop antenna is turned to a null position, comprising a plurality of conductor coil turns, means for accurately maintaining each conductor coil turn in a predetermined position, said means comprising a first group of four insulating corner spacing members, each one being located at a corner of said loop and having an aperture therein for each conductor turn to pass through, said apertures being arranged in the form of an ellipse, the conductor coil turns being wound so that each turn is located in an aperture on one insulating spacing corner member and progresses to an aperture in the next adjacent spacing corner member, said last mentioned aperture being spaced ninety degrees about the longitudinal axis of the loop coil in the plane of said second spacing corner member from the position of said aperture in the plane of said first mentioned spacing corner member, and a second group of insulating spacing members positioned intermediate said first mentioned insulating spacing members, an aperture in said second insulating spacing members for each conductor turn to pass through, said apertures being arranged in the form of a circle whose diameter is equal to the minor axis of said ellipse on said first mentioned insulating spacing members so as to maintain the diameter of the loop coil winding at intermediate points substantially constant.

2. A direction finder loop antenna having its winding of conductor turns transposed to give substantially zero energy pickup when said loop antenna is turned to a null position, comprising a plurality of conductor coil turns, means for accurately maintaining each conductor coil turn in a predetermined position, said means comprising a first group of four insulating spacing corner members, each one being located at a corner of said loop and having an aperture therein for each conductor turn to pass through, said apertures being arranged in the form of an ellipse, the conductor coil turns being wound so that each turn is located in an aperture on one insulating spacing corner member and progresses to an aperture in the next adjacent spacing corner member, said last mentioned aperture being spaced ninety degrees about the longitudinal axis of the loop coil in the plane of said second spacing corner member from the position of said aperture in the plane of said first mentioned spacing corner member, a second group of insulating spacing members positioned intermediate said first mentioned insulating spacing members, an aperture in said second insulating spacing members for each conductor turn, said apertures being arranged in the form of a circle whose diameter is equal to the minor axis of said ellipse on said first mentioned insulating spacing members so as to maintain the diameter of the loop coil winding at intermediate points substantially constant, a metallic casing substantially covering said loop, and a plurality of slots in said metallic casing for accurately retaining the first and second mentioned groups of insulating spacing members in a predetermined position.

BENJAMIN L. DOLBEAR. 

